Control valve arrangement

ABSTRACT

A control valve arrangement for use in controlling fuel pressure within a control chamber ( 30 ) includes a control valve member ( 32 ) which is movable between a first position in which the control chamber ( 30 ) communicates with a source of high pressure fuel, and a second position in which the control chamber ( 30 ) communicates with a low pressure fuel drain and communication between the control chamber ( 30 ) and the source of high pressure fuel is broken. The control valve arrangement also includes restricted flow means ( 55, 70, 86 ) for restricting the rate of flow of fuel from the control chamber ( 30 ) to the low pressure fuel drain when the control valve member ( 32 ) is moved from the first position to the second position. It is desirable for the restricted flow means to be configured and arranged such the rate of flow of fuel from the source of high pressure fuel to the low pressure drain for the period of time for which the control valve member ( 32 ) is moving between the second position and the first position is also restricted.

This invention relates to a control valve arrangement for use incontrolling fluid pressure within a control chamber. In particular, theinvention relates to a control valve arrangement for use in controllingfluid pressure within a control chamber forming part of a fuel injectorfor use in the delivery of fuel to a combustion space of an internalcombustion engine.

It is known to provide a fuel injector with a control valve arrangementwhich is arranged to control movement of a fuel injector valve needlerelative to a seating so as to control the delivery of fuel from theinjector. Movement of the valve needle away from the seating permitsfuel to flow from an injector delivery chamber through an outlet of theinjector into the engine cylinder or other combustion space.

The control valve arrangement includes a control valve member which ismovable between a first position, in which fuel under high pressure isable to flow into the control chamber, and a second position in whichthe control chamber communicates with a low pressure fuel reservoir. Asurface associated with the valve needle is exposed to fuel pressurewithin the control chamber such that the pressure of fuel within thecontrol chamber applies a force to the valve needle to urge the valveneedle against its seating.

In order to commence injection, the valve arrangement is actuated suchthat the control valve member is moved into its second position, therebycausing fuel pressure within the control chamber to be reduced. Theforce urging the valve needle against its seating is therefore reducedand fuel pressure within the delivery chamber serves to lift the valveneedle away from its seating to permit fuel to flow through the injectoroutlet. In order to terminate injection, the valve arrangement isactuated such that the control valve member is moved into its firstposition, thereby permitting fuel under high pressure to flow into thecontrol chamber. The force acting on the valve needle due to fuelpressure within the control chamber is therefore increased, causing thevalve needle to be urged against its seating to terminate injection.

For optimal injector performance, it is desired to control the rate atwhich the valve needle of the injector lifts so as to provide acontrolled increase in injection rate. However, it is also desired toterminate injection rapidly.

It is known to provide a restricted flow path so that the rate of flowof fuel between the source of high pressure fuel and the control chamberis restricted. This alleviates the problem of unbalanced hydraulicforces acting on the control valve member as a result of the flow offuel past the valve seat. Such unbalanced forces can cause the valveneedle of the injector to ′dither between injecting and non-injectingpositions, and this has a detrimental effect on injector performance.

A disadvantage of this restricted flow path is that it slows down therate at which the control chamber is pressurised, and therefore the rateat which the valve needle of the injector is urged against its seatingto terminate injection. Furthermore, depressurisation of the controlchamber can occur rapidly, giving rise to relatively fast valve needlelift. Such characteristics are not considered to provide optimalinjector performance.

It is an object of the present invention to provide a control valvearrangement suitable for use in a fuel injector, which enables animproved injection characteristic to be achieved.

According to a first aspect of the present invention there is provided acontrol valve arrangement for use in controlling fuel pressure within acontrol chamber, the control valve arrangement including a control valvemember which is movable between a first position in which the controlchamber communicates with a source of high pressure fuel and a secondposition in which the control chamber communicates with a low pressurefuel drain and communication between the control chamber and the sourceof high pressure fuel is broken, and restricted flow means forrestricting the rate of flow of fuel from the control chamber to the lowpressure fuel drain when the control valve member is moved from thefirst position to the second position.

The control valve arrangement has particular application in a fuelinjector, and may be arranged to control fuel pressure within a controlchamber associated with an injector valve needle so as to controlmovement of the valve needle towards and away from a valve needleseating for the purpose of controlling injection.

One advantage is that the restricted flow from the control chamber tothe low pressure drain results in a slower decrease in pressure withinthe control chamber. As a result, the speed with which the valve needleof the injector lifts away from its seating is slower and can bedetermined by selection of a suitable size of restriction.

Preferably, the restricted flow means is further operable forrestricting the rate of flow of fuel from the source of high pressurefuel to the low pressure drain when the control valve member is beingmoved between the second position and the first position. This providesthe advantage that, during the relatively brief period when the controlvalve arrangement is being switched between its first and secondpositions, the flow of fuel between the high pressure source and the lowpressure drain is restricted so as to minimise parasitic fuel losses.

In a more preferred embodiment, the restricted flow means is arranged sothat fuel flow rate out of the control chamber to the low pressure drainis relatively low whereas the fuel flow rate into the control chamberfrom the high pressure fuel source is relatively high. Thus, the rate offlow of fuel into the control chamber to terminate injection issubstantially unaffected by the restricted flow means and so terminationof injection can be achieved rapidly, providing asymmetric needle liftand closure rates.

The rate of flow of fuel through the control valve arrangement as thecontrol valve member is moved is determined by the pressure differencebetween the high pressure source and the low pressure drain, and by thesize of any restriction to flow. The unbalanced hydraulic forces whichgive rise to the aforementioned dithering problem are caused by a highrate of flow of fuel in this condition. The present arrangementovercomes the “dithering” problem at the same time as providing aslower, more controlled lifting of the valve needle in the injector foroptimal injector performance. The invention therefore also permits moreaccurate control over the injection of low delivery flows at smallvalues of needle lift.

In a preferred embodiment, the valve member engages with a first seatingwhen in the first position and with a second seating when in the secondposition.

In one embodiment, the first seating is defined by a surface of a boreprovided in a valve housing within which the valve member is movable.The second seating may also be defined by surface of the bore providedin the valve housing.

The restricted flow means may comprise a restricted flow passage definedby an outer surface of the valve member and the bore in the valvehousing. In one embodiment, the restricted flow passage is locatedbetween the first seating and the second seating.

Conveniently, the valve member and the valve housing together define aflow passage between the first seating and the second seating, whereinthe flow passage is provided with the restricted flow means upstream ofthe first seating, said restricted flow means preferably taking the formof a restricted clearance between a bore in the valve housing and anouter surface of the valve member.

The valve member may be shaped such that the restricted passage isdefined by control flats, slots or grooves on the outer surface of thevalve member, together with the bore in the valve housing.

In an alternative embodiment, the restricted flow means is arrangeddownstream of the first seating, in between the first seating and thelow pressure drain.

In an alternative embodiment, the restricted flow means may be definedby an orifice or restricted drilling provided in the valve member. Theorifice or restricted drilling may be provided in a region of the valvemember downstream of the first seating.

The bore in the valve housing may be provided with a sleeve or insertmember, wherein the sleeve defines the first seating and/or the secondseating.

The valve member may be provided with a collar having a slidable fitwithin a sleeve bore and may be shaped to define a recess between thefirst seating and the collar. The collar may be integrally formed withthe valve member, or may be a separate part carried by the valve member.Preferably, the orifice in the valve member may open into the recess.

A particular benefit of this embodiment is that the size of therestriction to flow depends upon the size of a single machine operation(the formation of the drilling defining the orifice).

In an alternative preferred embodiment, the control valve arrangementincludes a by pass flow means arranged within the control chamber.Preferably the by pass flow means includes a plate valve arrangementincluding a plate valve member provided with a control orifice extendingtherethrough. Preferably, a wall of the control chamber defines a platevalve seating, whereby the plate valve member is moveable against theplate valve seating by means of fuel pressure within the controlchamber, so as to ensure the flow of fuel from the control chamber flowsthrough the control orifice when the plate valve member is engaged withthe plate valve seating.

Preferably, the control chamber is shaped to define a bypass flowpassage around the plate valve member, whereby a substantiallyunrestricted flow of fuel can enter the control chamber when the platevalve member is urged away from the plate valve seating.

According to a second aspect of the present invention there is provideda fuel injector for use in delivering fuel to an internal combustionengine comprising a valve needle which is engageable with a valve needleseating, in use, to control fuel delivery through an outlet opening, asurface associated with the valve needle being exposed to fuel pressurewithin a control chamber, and a control valve arrangement forcontrolling fuel pressure within the control chamber as hereinbeforedescribed in accordance with the invention.

Preferably, when the control valve member is in its first position, thevalve needle is seated against the valve needle seating due to high fuelpressure within the control chamber, such that fuel injection does notoccur.

According to a third aspect of the present invention there is provided afuel injection system for an internal combustion engine comprising afuel injector as hereinbefore described in accordance with theinvention.

According to a fourth aspect of the present invention, there is provideda fuel injector for use in delivering fuel to an internal combustionengine, the fuel injector comprising a valve needle which is engageablewith a valve needle seating, in use, to control fuel delivery through anoutlet opening, a surface associated with the valve needle being exposedto fuel pressure within a control chamber, a control valve arrangementfor controlling fuel pressure within the control chamber so as tocontrol fuel injection and a further valve arrangement which is operablein response to fuel pressure within the control chamber so as to permita restricted flow of fuel out of the control chamber during valve needlelift and an increased flow of fuel into the control chamber duringpressurisation of the control chamber to terminate injection.

It will be appreciated that the preferred and/or optional features ofthe first aspect of the invention may also be incorporated in the otheraspects of the invention.

The invention will be described, by way of example, with reference tothe accompanying drawings, in which:

FIG. 1 is a sectional view of a known fuel injector which may beprovided with the control valve arrangement of the present invention,

FIG. 2 is a sectional view of a known control valve arrangement for usein the injector in FIG. 1,

FIG. 3 is a sectional view of part of a control valve arrangementforming part of a first embodiment of the invention,

FIG. 4 is a sectional view of part of a control valve arrangementforming part of a second embodiment of the invention,

FIG. 5 is a sectional view of a part of a control valve arrangementforming part of a third embodiment of the invention, and

FIG. 6 is a sectional view of part of a control valve arrangementforming part of a fourth embodiment of the invention.

Referring to FIG. 1, a fuel injector for use in delivering fuel to anengine cylinder or other combustion space of an internal combustionengine comprises a valve needle 10 which is slidable within a bore 12provided in a nozzle body 14. The valve needle 10 is engageable with avalve needle seating 16 defined by the bore 12 so as to control fueldelivery through a set of outlet openings 18 provided in the nozzle body14. The bore 12 is shaped to define an annular chamber 20 to which fuelunder high pressure is delivered, in use, through a supply passage 22provided in the nozzle body 14. Fuel delivered to the annular chamber 20is able to flow through flats, grooves or flutes 24 provided on thesurface of the valve needle 10 into a delivery chamber 26 definedbetween the valve needle 10 and the bore 12.

At the end of the valve needle 10 remote from the outlet openings 18,the end surface 10 a of the valve needle 10 is exposed to fuel pressurewithin a control chamber 30. Fuel pressure within the control chamber 30applies a force to the valve needle 10 which serves to urge the valveneedle 10 against the valve needle seating 16 to prevent fuel injectionthrough the outlet openings 18. In use, with high pressure fuel suppliedto the annular chamber 20 through the supply passage 22 and, hence, tothe delivery chamber 26, a force is applied to thrust surfaces 10 b 10 cof the valve needle 10 which serves to urge the valve needle 10 awayfrom the valve needle seating 16. If fuel pressure within the controlchamber 30 is reduced sufficiently, the force acting on the thrustsurfaces 10 b, 10 c due to fuel pressure within the delivery chamber 26is sufficient to overcome the force acting on the end surface 10 a ofthe valve needle 10, such that the valve needle 10 lifts away from thevalve needle seating 16 to commence fuel injection. Thus, by controllingfuel pressure within the control chamber 30, initiation and terminationof fuel injection can be controlled.

The pressure of fuel within the control chamber 30 may be controlled bymeans of the control valve arrangement, as shown in FIG. 2. The controlvalve arrangement includes a control valve member 32 which is slidablewithin a further bore 34 defined in a valve housing 36. The valvehousing 36 is in abutment with a further housing 40 within which thecontrol chamber 30 is defined, at least in part. The further housing 40is provided with a drilling which defines a flow passage 42 incommunication with a low pressure fuel reservoir or drain.

The end face of the further housing 40 defines a first seating 38 withwhich an end of the control valve member 32 is engaged when the controlvalve member 32 is moved into a first position. The further bore 34 isshaped to define a second seating 44 with which a surface of the controlvalve member 32 is engaged when the control valve member 32 is movedinto a second position. Conveniently, the control valve member 32 isbiased into engagement with the first seating 38 by means of a spring(not shown) or other biasing means. Movement of the control valve member32 may be controlled by means of an electromagnetic actuator arrangementor a piezoelectric actuator arrangement in a conventional manner.

It will be appreciated that the high pressure supply passage 22 isdefined by drillings provided in various housing parts (e.g. 14 in FIG.1, 40 in FIG. 2).

In use, with the control valve member 32 in its first position such thatthe end of the control valve member 32 is in engagement with the firstseating 38, fuel at high pressure is able to flow from the supplypassage 22 through an intermediate flow passage 46 defined in the valvehousing 36, past the second seating 44 and into the control chamber 30.In such circumstances, fuel pressure within the control chamber 30 isrelatively high such that the valve needle 10 is urged against the valveneedle seating 16. Thus, fuel injection through the outlet openings 18does not occur. The control valve member 32 is shaped such that a flowpath of relatively large diameter exists for fuel flowing through theintermediate flow passage 46, past the second seating 44 and into thecontrol chamber 30 when the control valve member 32 is seated againstthe first seating 38.

When the control valve member 32 is moved away from the first seating 38into engagement with the second seating 44, fuel within the supplypassage 22 is no longer able to flow past the second seating 44 and fuelwithin the control chamber 30 is able to flow past the first seating 38and through the flow passage 42 to the low pressure fuel reservoir. Fuelpressure within the control chamber 30 is therefore reduced. As aresult, the valve needle 10 is urged away from the valve needle seating16 due to the force of fuel pressure within the delivery chamber 26acting on the thrust surfaces 10 b and 10 c of the valve needle beingsufficient to overcome the reduced force acting on the end surface 10 aof the valve needle 10.

Referring to FIG. 3, in which equivalent features have the samereference numerals as those of FIG. 2, the valve member 32 is providedwith a portion 50, located between the first seating 38 and the secondseating 44, having a cylindrical outer surface 52. The further bore 34in the valve housing 36 includes a portion between the first seating 38and the second seating 44 having an internal cylindrical surface 54. Thecylindrical surface 52 of the valve member 32 and the cylindricalsurface 54 of the bore 34 together define a restricted flow passage orpath 55 between the first seating 38 and second seating 44. The controlchamber 30 communicates, via an extended passage 58 provided in thehousings 36,40, with an annular gallery 56 defined within the furtherbore 34. The diameter of the bore 34 is substantially identical to thediameter of the first seating 38, due to the “cut away” portion of thevalve member 32 at its lower end.

In use, when the valve member 32 is in engagement with the first seating38, spaced away from the second seating 44, the control chamber 30 is incommunication with high pressure fuel, and the valve needle 10 of theinjector is urged against the injector seating 16. When the valve member32 is lifted away from the first seating 38 and moves towards the secondseating 44, high pressure fuel flows through the extended passage 58,into the gallery 56 and through the restricted flow passage 55 to thelow pressure drain, and a point will be reached at which pressure in thecontrol chamber 30 is relieved sufficiently to permit the valve needle10 to lift. The restricted flow of fuel through the restricted passage55 during valve needle lift causes the pressure in the control chamber30 to fall more slowly than in the prior art arrangements, giving riseto a slower opening of the valve needle 10 of the injector.

When the valve member 32 is moved back into engagement with the firstseating 38, the pressure of fuel in the control chamber 30 rises rapidlyas the flow of high pressure fuel into the control chamber 30 does notpass through the restricted passage 55. Termination of injection istherefore rapid as the pressure in the control chamber 30 urges thevalve needle 10 of the injector against its seating 16.

As the valve member 32 moves between its second position (engagementwith the second seating 44) and its first position (engagement with thefirst seating 38), any flow of high pressure fuel past the secondseating 44 to low pressure is restricted by the restricted flow passage55. In known arrangements, while the valve member 32 is moving betweenthese positions, the rate of flow of fuel is determined by the pressuredifference between the high pressure supply (through 34) and the lowpressure drain (through 42) and the unbalanced hydraulic forces whichgive rise to the aforementioned “dithering” problem are caused by a highrate of flow of fuel to low pressure. The “dithering” problem isovercome by the present arrangement as the rate of flow of high pressurefuel to low pressure as the valve member 32 is moving from its secondseating 44 to its first seating 38 is restricted by means of the passage55. At the same time, however, the benefits of a rapid termination ofinjection can also be achieved. This is another advantage of the presentinvention, as the flow rate of high pressure fuel out of the controlchamber 30 to low pressure so as to lift the valve needle is relativelylow due to the restricted passage 55, whereas the flow rate of fuel intothe control chamber 30 to terminate injection is relatively high, as theflow rate to terminate injection is not hindered by the restrictedpassage 55. The valve needle therefore has an asymmetry in its rate ofopening and rate of closing movement.

As a slight modification, the valve member 32 may be provided withflats, slots or grooves on its outer surface to define the restrictedflow passage for fuel between the control chamber and the low pressuredrain during needle lift.

For low values of needle lift (i.e. when the valve member is at or nearthe first seating 38), the hydraulic forces acting on the valve member32 are substantially balanced, but for intermediate values of needlelift, as the valve member 32 is moving between its first seating 38 andits second seating 44, there will be a force imbalance acting on thevalve member 32 as the control pressure due to flow from the controlchamber 30 is still relatively high. At or near full needle lift, withthe valve member 32 at or near the point of engagement with its secondseating 44, control pressure is substantially reduced and the valvemember 32 is balanced once again. As a result of the flow-dependentimbalance of forces acting on the valve member 32, movement of the valvemember 32 will be slowed as it approaches the second seating 44. As itapproaches the first seating 38 to terminate injection, the rate ofmovement of the valve member 32 will be increased. This asymmetry is adesirable characteristic.

Referring to FIG. 4, in which equivalent features have the samereference numerals as those of FIGS. 2 and 3, an alternative arrangementis shown in which the first seating 38 is defined by an end face of asleeve 60 or “floating seat” inserted into the bore 34 of the housing36. A lower portion 62 of the valve member 32 is provided with a collar64, having an outer cylindrical surface, which forms a slidable fitwithin a bore 66 of the sleeve 60. The valve member 32 is also shaped todefine an annular recess 68, located upstream of the collar 64, in fluidcommunication with the low pressure drain passage 42 via an orifice 70and a blind drilling 72 provided in the lower region 62 of the valvemember 32. The orifice 70 has a diameter, which is selected to provide arestriction to fuel flow therethrough.

As shown in FIG. 4, when the valve member 32 is in the second positionin which it engages the second seating 44, the control chamber 30 is influid communication with the low pressure drain so that fuel can flowpast the first seating 38 into the recess 68, through the orifice 70 andthe drilling 72 to the low pressure drain 42. The orifice 70 thereforeprovides the same flow restricting effect as the restricted passage 55of the embodiment of FIG. 3, resulting in a slower fall of pressure inthe control chamber 30 as the valve member 32 is moved from its firstposition (engagement with the first seating 38) into its second position(engagement with the second seating 44).

Similarly, when the valve member 32 is moved out of engagement with thesecond seating 44, the pressure of fuel within the control chamber 30rises rapidly. While the valve member 32 moves between the secondseating 44 and the first seating 38, and just prior to the valve member32 seating against the first seating, the flow of high pressure fuelpast the second seating 44 is restricted by the orifice 70 to avoid orreduce the problem of dithering.

FIG. 5 shows a further alternative embodiment to that shown in FIGS. 3and 4. In this embodiment, the first seating 38 for the valve member 32is of greater diameter than the diameter of the bore 34 defining thesecond seating 44 but is the same as the diameter of the valve member 32at an outer radial edge 44 a of the seatable surface of valve member 32.The valve arrangement also includes a force balance arrangementincluding a balance piston 60 received within a blind drilling 75provided in the lower end of the valve member 32. The blind drilling 75defines, at one end thereof, a blind end space or volume 72 whichcommunicates, through a radially extending drilling 70, with an annularchamber 71 defined by an enlarged region of the bore 34. The other endof the drilling 72 opens into a further space 73. The annular chamber 71communicates with the control chamber 30 through drillings 81, 82provided in various housing parts.

As described previously with reference to FIG. 3, the outer surface ofthe lower end of the valve member 32 and the bore 34 in the valvehousing 36 together define a restricted flow passage 55 which serves torestrict the rate of flow of fuel between the control chamber and thelow pressure drain when the valve member 32 is moved away from the firstseating 38. Alternatively, the valve member 32 may be provided withcontrol flats (as illustrated in dashed lines) on its outer surface todefine the restricted flow passage.

In use, as the valve member 32 is biased away from the second seating44, into engagement with the first seating 38, the seatable surface ofthe valve member 32 is exposed to high pressure fuel flow between thesupply passage 22 and the control chamber 30. In the absence of theforce balance arrangement 60, 72, 70, 75, this exposed surface of thevalve member 32 would experience a force due to hydraulic pressure thatwould tend to aid movement of the valve member 32 towards the firstseating 38. However, due to the provision of the force balancearrangement 60, 72, 70, 75, as the valve member 32 is moved away fromthe seating 44 fuel is able to flow into the volume 72 through thedrilling 70. The force balance arrangement is dimensioned such that thehydraulic forces acting on the valve member 32 within the volume 72tends to balance the out of balance force acting on the exposed valvesurface.

During movement of the valve member 32 between the second and firstseatings 44, 38 to seat the valve needle, the hydraulic forces acting onthe valve member 32 are therefore substantially balanced. Although notclearly shown in FIG. 5, the balance piston 60 should be dimensioned tobe a relatively tight fit within the drilling 72 so as to minimise fuelleakage loss to low pressure during termination of injection. Referringto FIG. 6, in another embodiment the control chamber 30 includes a platevalve arrangement 80 which is operable in response to fuel pressurewithin the control chamber 30. The plate valve arrangement 80 may beprovided in combination with the control valve arrangement of FIG. 2, orin combination with the control valve arrangement of FIG. 3 or 4. Theplate valve arrangement 80 has a plate valve member 82 having first andsecond end faces 84, 88 and a control orifice 86 extending through theplate valve member 82 between the end faces 84, 88. The wall of thecontrol chamber 30 is shaped to define a plate valve seating 90 for thefirst end face 84 of the plate valve member 82, and an annular recessdefining a bypass flow passage 92 around the plate valve member 82.Although not shown in FIG. 6, the plate valve arrangement may beprovided with a spring to bias the plate valve member 82 towards theplate valve seating 90.

In use, when the control valve member 32 of FIG. 2 is seated against thefirst seating 38, fuel pressure within the control chamber 30 is highand the valve needle 10 of the injector is seated. When the controlvalve member 32 is lifted away from the first seating 38, the controlchamber 30 is brought into communication with the low pressure drainpassage 42. The pressure of fuel in the control chamber 30 serves tourge the plate valve member 82 against the plate valve seating 90 sothat fuel can only escape from the control chamber through the controlorifice 86 in the plate valve member 82 at a controlled rate. Thisresults in a slower lifting of the injector valve needle 10 away fromits seating 16.

When the control valve member 32 is moved away from the second seating44 back towards the first seating 38, high pressure fuel is able to flowinto the control chamber 30. As high pressure fuel is re-establishedwithin the control chamber 30. the plate valve member 82 is urged awayfrom the plate valve seating 90 to permit a rapid flow of high pressurefuel around the plate valve member 82 through the bypass flow passage92, thereby imparting a hydraulic force to the back end of the valveneedle 10. The provision of the plate valve arrangement thereforeenables rapid re-pressurisation of the control chamber 30 when injectionis to be terminated. Thus, rapid closure of the injector valve needle 10can be achieved.

In an alternative embodiment to that shown in FIG. 6, the plate valvemember 82 may be replaced by an alternative fixed part provided with acontrol orifice 86 having an inlet end in communication with the pathfrom the valve (i.e. valve member 32 in FIGS. 3 to 6) and an outlet endin communication with the control chamber 30. The inlet end of thecontrol orifice 86 is radiused or bell or trumpet mouthed, and theoutlet end is sharp edged such that there is a greater restriction tothe fuel flow rate out of the control chamber 30 than into the controlchamber 30. This embodiment also therefore provides an asymmetric needlelift characteristic, as described previously for the embodiments ofFIGS. 3 to 6. The alternative part which replaces the plate valve member82 of FIG. 6 may be a separate component, or may form part of thehousing defining the walls of the control chamber 30.

1. A control valve arrangement for use in controlling fuel pressurewithin a control chamber, the control valve arrangement including acontrol valve member which is movable between a first position to engagea first seating in which the control chamber communicates with a sourceof high pressure fuel, and a second position to engage a second seatingin which the control chamber communicates with a low pressure fuel drainand communication between the control chamber and the source of highpressure fuel is broken, wherein the first seating is defined by asurface of a bore provided in a valve housing within which the controlvalve member is movable; and a restricted flow path for restricting therate of flow of fuel from the control chamber to the low pressure fueldrain when the control valve member is moved from the first position tothe second position, wherein the restricted flow path comprises arestricted flow passage being located between the first seating and thesecond seating.
 2. A control valve arrangement as claimed in claim 1,wherein the restricted flow path is further operable for restricting therate of fuel flow from the high pressure fuel source to the low pressuredrain when the control valve member is being moved between the secondposition and the first position, thereby to reduce the loss of highpressure fuel to low pressure.
 3. A control valve arrangement as claimedin claim 1 wherein the restricted flow path is arranged so that fuelflow rate out of the control chamber to the low pressure drain isrelatively low whereas the fuel flow rate into the control chamber isrelatively high, thereby providing asymmetric control valve operation.4. (canceled)
 5. A control valve arrangement as claimed in claims 1,wherein the control valve member is movable within the bore provided inthe valve housing and wherein an insert is arranged within the bore inthe valve housing to define the first seating.
 6. A control valvearrangement as claimed in claim 1 wherein the second seating is definedby surface of the bore provided in the valve housing.
 7. (canceled)
 8. Acontrol valve arrangement as claimed in claim 1, wherein the controlvalve member is shaped such that the restricted flow passage is defined,in part, by a control flat provided on the outer surface of the controlvalve member.
 9. (canceled)
 10. A control valve arrangement as claimedin claim 1, wherein the restricted flow path is arranged upstream of thefirst seating and downstream of the second seating.
 11. A control valvearrangement as claimed in claim 1, wherein the restricted flow path isarranged downstream of the first seating between the first seating andthe low pressure drain.
 12. A control valve arrangement as claimed inclaims 1, wherein the restricted flow path is defined by an orificeprovided in the control valve member.
 13. A control valve arrangement asclaimed in claims 1, wherein the control valve arrangement includes a bypass flow path arranged within the control chamber.
 14. A control valvearrangement as claimed in claim 13, wherein the by pass flow path isprovided with a plate valve arrangement including a plate valve memberprovided with a control orifice extending therethrough.
 15. A controlvalve arrangement as claimed in claim 14, wherein a wall of the controlchamber defines a plate valve seating, whereby the plate valve member ismoveable against the plate valve seating by means of fuel pressurewithin the control chamber, so as to ensure the flow of fuel from thecontrol chamber passes through the control orifice when the plate valvemember is engaged with the plate valve seating.
 16. A control valvearrangement as claimed in claim 15, wherein the control chamber isshaped to define a by pass flow passage around the plate valve member,whereby a substantially unrestricted flow of fuel can enter the controlchamber when the plate valve member is urged away from the plate valveseating.
 17. A fuel injector for use in delivering fuel to an internalcombustion engine, the fuel injector comprising a valve needle which isengageable with a valve needle seating, in use, to control fuel deliverythrough an outlet opening, a surface associated with the valve needlebeing exposed to fuel pressure within a control chamber, and a controlvalve arrangement as claimed in claim 1 for controlling fuel pressurewithin the control chamber.
 18. (canceled)
 19. A fuel injection systemfor an internal combustion engine comprising a fuel injector as claimedin claim 17.